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Optical biosensors have emerged in the past decade as the most promising candidates for portable, highly-sensitive bioanalytical systems that can be employed for in-situ measurements. In this work, a miniaturized optoelectronic system for rapid, quantitative, label-free detection of harmful species in food is presented. The proposed system has four distinctive features that can render to a powerful tool for the next generation of Point-of-Need applications, namely it accommodates the light sources and ten interferometric biosensors on a single silicon chip of a less-than-40mm2 footprint, each sensor can be individually functionalized for a specific target analyte, the encapsulation can be performed at the wafer-scale, and finally it exploits a new operation principle, Broad-band Mach-Zehnder Interferometry to ameliorate its analytical capabilities. Multi-analyte evaluation schemes for the simultaneous detection of harmful contaminants, such as mycotoxins, allergens and pesticides, proved that the proposed system is capable of detecting within short time these substances at concentrations below the limits imposed by regulatory authorities, rendering it to a novel tool for the near-future food safety applications.

Protein detection and characterization based on Broad-band Mach-Zehnder Interferometry is analytically outlined and demonstrated through a monolithic silicon microphotonic transducer. Arrays of silicon light emitting diodes and monomodal silicon nitride waveguides forming Mach-Zehnder interferometers were integrated on a silicon chip. Broad-band light enters the interferometers and exits sinusoidally modulated with two distinct spectral frequencies characteristic of the two polarizations. Deconvolution in the Fourier transform domain makes possible the separation of the two polarizations and the simultaneous monitoring of the TE and the TM signals. The dual polarization analysis over a broad spectral band makes possible the refractive index calculation of the binding adlayers as well as the distinction of effective medium changes into cover medium or adlayer ones. At the same time, multi-analyte detection at concentrations in the pM range is demonstrated.

The label-free detection of bovine milk in goat milk through a miniaturized optical biosensor is presented. The biosensor consists of ten planar silicon nitride waveguide Broad-Band Mach–Zehnder interferometers (BB-MZIs) monolithically integrated and self-aligned with their respective silicon LEDs on the same Si chip. The BB-MZIs were transformed to biosensing transducers by functionalizing their sensing arm with bovine k-casein. Measurements were performed by continuously recording the transmission spectra of each interferometer through an external spectrometer. The amount of bovine milk in goat milk was determined through a competitive immunoassay by passing over the sensor mixtures of anti-k-casein antibodies with the calibrators or the samples. The output spectra of each BB-MZI recorded during the reaction were subjected to Discrete Fourier Transform in order to convert the observed spectral shifts to phase shifts in the wavenumber domain. The method had a detection limit of 0.04 % (v/v) bovine milk in goat milk, dynamic range 0.1–1.0 % (v/v), recoveries 93–110 %, and intra- and inter-assay coefficients of variation less than 12 and 15 %, respectively. The proposed biosensor compared well in terms of analytical performance with a competitive ELISA developed using the same monoclonal antibodies. Nevertheless, the duration of the biosensor assay was 10 min whereas the ELISA required 2 h. Thus, the fast and sensitive determinations along with the small size of the sensor make it ideal for incorporation into portable devices for assessment of goat or ewe’s milk adulteration with bovine milk at the point-of-need.[Figure not available: see fulltext.]

Miniaturized integrated thin-film biosensors were developed for use in clinical analyzers and for in vivo applications. A glucose and a lactate sensor were integrated with a pH-sensor on a flexible substrate. Both enzyme sensors are based on the electrochemical measurement of H2O2 produced by the enzymes glucoseoxidase and lactateoxidase respectively. The solid state pH-sensor uses a neutral carrier membrane. The intended application of this device is the monitoring of metabolic parameters in the intensive care unit and the operation theater and the use as a sensor module in clinical analyzers. The glucose-, lactate- and pH-sensor was tested in buffer solutions and undiluted serum showing excellent performance.

In this paper, we report on a thin film sensor for the detection of carbon dioxide dissolved in liquids with the attention focused on its use for clinical blood gas analysis. Carbon dioxide from the analyte penetrates into a hydrogel electrolyte through a gas permeable membrane and is chemisorbed on a rhodium working electrode. The concentration of CO2 collected by this way is determined by an amperometric measurement technique based on the inverse voltammetry.

There are several totally different definitions of the so-called ectopic anus. To determine whether computerized eight-channel manometry helps to define the entity of the ectopic anus, ten patients (nine females) were operated upon for an ectopic anus by the anal transposition technique (perineal pull-through procedure). Besides the software-supported manometric data, the qualitative imaging analysis was of interest. We calculated the factor by which the pressure of the three ventrally-located segments was lower than the mean segmental pressure at this part of the anal canal. The results were compared to standard age-related values established in a former study in 100 children. Besides pre- and postoperative manometry, barium roentgenograms were obtained. The anal-canal length at rest in the ectopic anus was significantly (P < 0.0001) longer. The segmental asymmetry index in the lower anal canal (LAC) was increased, but not significantly. The pressure in the ventral segments of the LAC was significantly (P < 0.0001) decreased and was less than one-half of the mean segmental pressure in this zone. We found a significant correlation between the degree of anterior displacement and the factor by which the ventrally-located pressure values were decreased. Postoperatively, this factor increased significantly. From a functional point of view, the definition of the ectopic anus includes a deficient high-pressure zone ventrally in the LAC. The LAC seems to run out or nearly out of the ventral sphincteric issue to end ectopically on the perineal surface.

The objective of the study was to evaluate the performance of an amperometric enzyme based lactate sensor and to investigate the possibility of replacing a double lumen catheter based blood withdrawal system with a heparin coated single lumen system. The inner lumen of a double lumen catheter which was placed in a peripheral vein was perfused with heparin solution. The outer lumen was used to collect heparinized blood samples at a defined flow rate. The single lumen system was attached to a heparinized catheter which was also placed in a peripheral vein. The undiluted blood samples were collected at a specified flow rate. A sensor flow chamber incorporating an amperometric thin-film lactate microbiosensor was placed in the sampling line for real-time lactate monitoring. Plasma lactate concentrations were measured during frequently performed hyperlactatemia bicycle ergometer experiments in six healthy volunteers (age 25.8 +/- 2.8 years, BMI 22.7 +/- 1 kg/m2). Additionally, plasma lactate was measured in real-time using the lactate sensors. The first three experiments were performed with a double lumen based catheter system whereas the following three experiments were performed with a heparin coated catheter system. The correlation coefficients of sensor readings and laboratory analyzer results in all six experiments were between 0.93 and 0.99, respectively (P < 0.001). The miniaturized lactate sensors showed a linear range up to 25 mmol/l lactate concentration and 95% response times < 30 s in undiluted serum. During the experiments maximum lactate concentrations of 14 mmol/l were achieved. Improvements of system performance using heparin coated catheter systems could be shown. The overall SD of the sensor readings compared to laboratory results using three double lumen catheter based systems was 0.91 mmol/l whereas the SD using three heparin coated systems was 0.65 mmol/l. In summary, real-time monitoring of lactate in human whole blood is feasible with such a device and can be improved by using heparin coated catheter systems.

The present study was carried out to investigate in vivo in healthy humans the method of open-flow microperfusion for monitoring of the subcutaneous (s.c.) lactate concentration during rest and cycle ergometer exercise. Using open-flow microperfusion, a perforated double lumen catheter with an inflow and an outflow connection is inserted into the s.c. adipose tissue and perfused with a sterile, isotonic, ionfree fluid. Due to the low flow rate, the fluid partially equilibrates with the surrounding tissue. The equilibrated perfusate passes a sensor flow chamber where the substance of interest and the rate of recovery (i.e. the ratio of sampled concentration to interstitial concentration) are continuously monitored. Within this study, the method was evaluated in four healthy volunteers during cycle ergometer exercise. The relative increase of the lactate concentration was approximately a third in the s.c. tissue compared to the capillary blood and the peak time was delayed on average by 10 min. The correlation coefficient between blood and s.c. tissue lactate concentration ranged from r = 0.41 to r = 0.90 (n = 29) in the individual experiments. The combination of open-flow microperfusion and lactate and conductivity sensors enables on-line monitoring of the s.c. lactate concentration without in vivo calibration during steady-state and cycle ergometer exercise.

Integrated optical sensor chips suitable for high-resolution pH measurements are presented. The pH-sensitive swelling of a polymer membrane is detected by refractometry using a compact multi-channel sensor module. The signal transduction is achieved by means of chirped grating couplers which allow simple yet high functionality sensor modules to be built. The experiments have been performed with high sensitivity replicated polycarbonate TiO2 waveguide sensor chips coated with an ultrathin photopatterned hydrogel membrane having functional groups which reversibly change from the neutral state to a charged state upon acidification. A resolution δpH

Conductometric measurements are of interest in analytical chemistry. They provide an overall-sight of the ionic strength in electrolytes and can be used for analytical purposes if they are provided with a selectivity factor, e.g. enzyme membranes. Miniaturised transducers were formed by means of photolithography, thin film, and plasma technologies. Two- and 4-electrode measurements were taken to characterise sensitivity and dynamic range. However, using 4-electrode measurements expands the dynamic range from deionised water up to 1 mol KCl-solution and increases the sensitivity at high background conductivity. Such measurements were taken out with electrodes which had an interdigital distance of 50 μm and an area of 0.04 mm2. Additionally, interdigital structures with interdigital distances of 5 μm were investigated. Coated with a poly-HEMA membrane wherein urease was immobilised, a urea sensor was constructed. The concentration-range of urea was 1–30 mmol urea in 20 mmol HEPES-buffer.

Miniaturized bioanalytical devices find wide applications ranging from blood tests to environmental monitoring. Such devices in the form of hand held personal laboratories can transform point-of-care monitoring provided miniaturization, multianalyte detection and sensitivity issues are successfully resolved. Optical detection in biosensors is superior in many respects to other types of sensing based on alternative signal transduction techniques, especially when both sensitivity and label free detection is sought. The main drawback of optical biosensing transducers relates to the unresolved manufacturability issues encountered when attempting monolithic integration of the light source. If the mature silicon processing technology could be used to monolithically integrate optical components, including light emitting devices, into complete photonic sensors, then the lab on a chip concept would materialize into a robust and affordable way. Here, we describe and demonstrate a bioanalytical device consisting of a monolithic silicon optocoupler properly engineered as a planar interferometric microchip. The optical microchip monolithically integrates silicon light emitting diodes and detectors optically coupled through silicon nitride waveguides designed to form Mach-Zehnder interferometers. Label free detection of proteins is demonstrated down to pM sensitivities.

Despite the advances in optical biosensors, the existing technological approaches still face two major challenges: the inherent inability of most sensors to integrate the optical sourc e in the transducer chip, and the need to specifically design the optical transducer per application. In this work, the development of a radical optoelectronic platform is demonstrated based on a monolithic optocoupler array fabricated by standard Si-technology and suitable for multi-analyte detection. The platform has been specifically designed biochemical sensing. In the all-silicon array of transducers, each optocoupler has its own excitation source, while the entire array share a common detector. The li ght emitting devices (LEDs) are silicon avalanche diodes biased beyond their breakdown voltage and emit in the VIS -NIR part of the spectrum. The LEDs are coupled to individually functionalized optical transducers that converge to a single detector for multiplexed operation. The integrated nature of the basic biosensor scheme and the ability to functionalize each transducer independently allows for the development of miniaturized optical transducers tailored towards multi -analyte tests. The monolithic arrays can be used for a plethora of bio/chemical interactions becoming thus a versatile analytical tool. The platform has been successfully applied in bioassays and binding in a real -time and label-free format and is currently being applied to ultra-sensitive food safety applications.

Glucose monitoring is at present the most widespread application of the GOD/H 2 O 2 system. This paper deals with a new technique for immobilizing onto electrochemical thin-film electrode cells based on this detection principle. The thin-film structure consists of a 100 nm thick titanium—platinum or —palladium sandwich layer on glass substrates isolated by a 3 μm silicon nitride film. A three-electrode miniaturized electrochemical cell with an outer diameter of 200 μm was produced by means of standard wet and dry etching procedures. The Ag/AgCl reference electrode was produced by depositing and structuring a 1 μm thick silver film which was subsequently chlorinated by FeCl 3 . The Pt or Pd surface was oxidized electrochemically in dilute aqueous oxidizing solutions. The modified surface was derivatized with amino-organic silylating agents. The covalent coupling of glucose oxidase was carried out by introducing a substituted bifunctional 1,4-benzoquinone group between the silylated electrode surface and the enzyme. A sulfonated polymer was used to protect the enzyme layer and to modify the diffusion characteristics of the electrode.

A sensorchip with an integrated flow cell with a volumina of 1 /spl mu/l provided the possibility of simultaneous measurement of four different parameters. Integrated thin film biosensors for simultaneous measurement of glucose, lactate, glutamine, and glutamate were combined to a biosensor array. Due to a novel glutaminase with an activity optimum in the neutral pH range direct and simultaneous monitoring of glutamine together with glucose, lactate, and glutamate could be performed during mammalian cell culture.

A foil-based BioMEMS for electrochemical capillary immunoassay for hepatitis serology is presented. Immobilization of the hepatitis antigen utilizing capillary forces and special stopping barriers in foil based microsystems and the application of it in fast immunoassays will be shown. The measurement starts with the addition of the antibody containing human serum sample. Subsequently the signal antibody labelled with glucose oxidase binds to the hepatitis B antibody and converts glucose to hydrogen peroxide, which is oxidized at the electrode in the measurement cell. The assay is very sensitive and designed to differentiate between hepatitis B negative (below 10 U/l) and positive serum. The present limit of detection of immunoassays in the BioMEMS is 20 atto-moles.

The simultaneous on-line determination of glucose and lactate using a microdevice that consisted of a dialysis sampling system incorporated to the flow-through cell of a microfabricated biosensor array is presented. The fluidic connections between the different device's components were realized by subsequent processing of stacked dry resist layers on a plastic support that provided also the means for electric connections. The performance of the device was evaluated in vitro. The cross-talk effect on the downstream sensor was investigated and found to be negligible. Recoveries of over 95% for both analytes were achieved when flow rates of the perfusion fluid ≤0.5 μl/min were used. At this flow rate, the response time of the device was 2.4 min, which is acceptable for on-line analysis. The linear response concentration range extended up to 30 mM for glucose and 15 mM for lactate. Interference from electroactive species such as ascorbic acid, 2-acetamidophenol and uric acid, was minimal (less than 5% increase in biosensors signal for all substances tested). In addition, the device presented long-term run stability both in buffer and serum samples.

The fabrication of a microdevice for continuous sampling and on-line monitoring of glucose is described. The device comprised a microdialysis sampling system integrated on the flow through channel of a microfabricated enzyme sensor. The sensor was produced by thin film technology and was assembled to a printed circuit board (PCB) that provided the means for both electrical and fluidic connections. A polyacrilonitrile fibre, with a cut-off of 50 kDa, was used in the fabrication of the sampling probe. The performance of the device was evaluated in-vitro. High sampling efficiency of the microdialysis probe was achieved by appropriate selection of the perfusion fluid flow rate. Response times varying from 1.5 to 3.0 min were determined for flow rates ranging between 1 and 0.2 μl/min. The linear response range was up to 30 mM glucose and interference from other electroactive substances was almost negligible. The device showed excellent stability under continuous operation for at least 5 days and sensitivity variation less than 3% over a period of 15 days.

A complete Mach-Zehnder interferometer monolithically integrated on silicon is presented and employed as a refractive index and bio-chemical sensor. The device consists of broad-band light sources optically coupled to photodetectors through monomodal waveguides forming arrays of Mach-Zehnder interferometers, all components being monolithically integrated on silicon through mainstream silicon technology. The interferometer is photonically engineered in a way that the phase difference of light travelling through the sensing and reference arms is approximately wavelength independent. Consequently, upon effective medium changes, it becomes feasible even with a broad-band source to induce sinusoidal-type of detector photocurrents similar to the classical monochromatic counterparts. The device is completed with its fluidic and interconnect components so that on chip interferometric measurements can be performed. Examples of refractive index and protein sensing are presented to establish the potential of the proposed device for real-time in situ monitoring applications. This is the only silicon device that has achieved complete on-chip interferometry.

A miniaturised flow-through biosensor with a cell volume of only a few nanoliters was developed in our laboratory. The biosensor can be directly coupled to a microdialysis or ultrafiltration probe. Sampling and continuous on-line monitoring can thus be carried out at submicroliter levels and as a consequence quantitative recoveries of the analyte of interest are achieved. Via this method excessive calibration procedures, as are necessary with conventional microdialysis, are avoided. Here, the construction and the performance of such a biosensor for the continuous on-line monitoring of glucose and lactate will be presented. The biosensor is based on the amperometric detection of hydrogen peroxide after conversion of the analyte of interest by an immobilised oxidoreductase enzyme. Immobilisation of the enzyme is performed through electropolymerisation of m-phenylenediamine. Strategies to improve the performance (e.g. linearity, selectivity and stability) of the miniaturised biosensor are discussed and ex vivo and in vivo experiments carried out thus far demonstrate the potential of this miniaturised flow-through biosensor.

Lactate dehydrogenase catalyzes the final step in glycolysis, the interconversion of pyruvate and lactate. The tetrameric enzyme is composed of one or two subunits (H and/or M) resulting in five isoenzyme forms: LDH-H4, -H3M1, -H2M2, -H1M3, and -M4. The relative distribution of the LDH isoenzymes is tissue dependent and a significant marker for the diagnosis of hepatoma of the liver, myocardial infarction, muscular dystrophy, and a wide variety of other acute and chronic diseases to be detected by alterations of the LDH isoenzyme pattern in serum. Immunochemical approaches to the routine determination of LDH depend on isoenzyme specific antibodies. Since the H- and M-subunits for human LDH are highly homologous, LDH isoenzyme specific antibodies for immunochemical monitoring are hard to generate. Here we present data on the generation and characterization of LDH isoenzyme-specific mono- and polyclonal antibodies in different species in the presence of lipopeptide adjuvants. Western-Blot and ELISA analysis showed that antisera and monoclonal antibodies recognize their homologous antigens with high specificity and are therefore suitable for immunochemical monitoring of the LDH isoenzymes H4 and M4. In addition, they can be used for the determination of LDH isoenzyme specific activity which is an essential prerequisite for online amperometric immunosensor monitoring.

The objective of the study was to evaluate the performance of an amperometric enzyme based lactate sensor and to investigate the possibility of replacing a double lumen catheter based blood withdrawal system with a heparin coated single lumen system. The inner lumen of a double lumen catheter which was placed in a peripheral vein was perfused with heparin solution. The outer lumen was used to collect heparinized blood samples at a defined flow rate. The single lumen system was attached to a heparinized catheter which was also placed in a peripheral vein. The undiluted blood samples were collected at a specified flow rate. A sensor flow chamber incorporating an amperometric thin-film lactate microbiosensor was placed in the sampling line for real-time lactate monitoring. Plasma lactate concentrations were measured during frequently performed hyperlactatemia bicycle ergometer experiments in six healthy volunteers (age 25.8 +/- 2.8 years, BMI 22.7 +/- 1 kg/m2). Additionally, plasma lactate was measured in real-time using the lactate sensors. The first three experiments were performed with a double lumen based catheter system whereas the following three experiments were performed with a heparin coated catheter system. The correlation coefficients of sensor readings and laboratory analyzer results in all six experiments were between 0.93 and 0.99, respectively (P0.001). The miniaturized lactate sensors showed a linear range up to 25 mmol/l lactate concentration and 95% response times30 s in undiluted serum. During the experiments maximum lactate concentrations of 14 mmol/l were achieved. Improvements of system performance using heparin coated catheter systems could be shown. The overall SD of the sensor readings compared to laboratory results using three double lumen catheter based systems was 0.91 mmol/l whereas the SD using three heparin coated systems was 0.65 mmol/l. In summary, real-time monitoring of lactate in human whole blood is feasible with such a device and can be improved by using heparin coated catheter systems.

A miniaturized microanalytical device for the simultaneous monitoring of different metabolites was realized by assembling of a biosensor array produced by thin film technology with a flow-through cell produced by printed circuit board technology. The biosensor array comprises four working electrodes which can be individually configured. Glucose and lactate devices were made for whole blood monitoring. Ex vivo experiments, performed on animals, where the device was continuously operated in an extracorporeal undiluted heparinized blood stream without loss in sensitivity for 48 hours, gave close tracing to routinely used clinical analyzers by using one point in vitro calibration.

For fast and continuous measurements of metabolic parameters small and easy-to-handle analytic devices with integrated chemo- and biosensors implemented in a fluidic microsystem were developed. Such microsystem was chosen for minimal invasive measurement, to overcome analyte handling problems and to perform continuous measurements.

A prototype miniaturized Total Chemical Analysis System (μTAS) has been developed and applied to on-line monitoring of glucose and lactate in the core blood of anaesthetized dogs. The system consists of a highly efficient microdialysis sampling interface sited in a small-scale extracorporeal shunt circuit (‘MiniShunt’), a silicon machined microflow manifold and integrated biosensor array for glucose and lactate detection with associated computer software for analytical process control. During in-vivo testing the device allowed real-time on-screen monitoring of glucose and lactate with system response times of less than 5 min, made possible by the small dead volume of the microflow system. On-line glucose and lactate measurements were made in the basal state as well as during intravenous infusion of glucose or lactate. The prototype μTAS is currently suitable for trend monitoring but refinements are necessary before application of the system for determination of individual lactate values.

In vielen Bereichen der Medizin, unter anderem in der Diabetologie und in der Intensivmedizin, wachst die Notwendigkeit, wahtige metabolische Parameter online messen zu konnen. Nur mit Monitoring und bettseitiger Analyse wahrend Operationen und in der Intensivstation lassen sich Konzentrationsschwankungen und Trends fruhzeitig und schnell erkennen. Zudem soll der Einsatz von in-vivo Sensoren auch die Untersuchung des lokalen Stoffwechsels auf kleinstem Raum im Gewebe ermoglichen. Um diesen Anforderungen gerecht werden zu konnen, bedarf es zuverlassiger, einfach handhabbarer und genauer Sensoren, die vorteilhafterweise zu integrierten Multisensoren kombiniert sein sollen. Die Bedeutung des Glukose-Laktat-Biosensors liegt in dem engen Zusammenspiel der beiden Substanzen in den Stoffwechselzyklen begrundet. Die Anordnung mehrerer, unabhangig arbeitender Biosensoren auf einem Trager verlangt eine ausreichende Miniaturisierbarkeit fur den in-vivo Einsatz. Die Anwendung fur diese Gebiete der Medizin schliest viele Konzepte makroskopischer Sensoren aus, deren Herstellung aufwendig und grostenteils manuell geschieht. Damit sich diese integrierten Sensoren auch am Markt durchsetzen konnen, ist auf eine kostengunstige Produktion zu achten. Die Miniaturisierung, Integration und die Moglichkeit zur Massenfertigung sind gute Voraussetzungen fur die Anwendung der Dunnschichttechnologie in der Sensortechnik.

Integrated and miniaturized biosensor arrays were developed exhibiting outstanding performance. Biosensors with negligible sensitivity to interferences and high long-term stability were produced by modifying electrochemical transducers and utilizing photopatternable enzyme membranes. The use of appropriate miniaturization technology leads to mass producible devices for in vivo and ex vivo applications.

Integrated thin film biosensors for simultaneous measurement of L-glutamine and L-glutamate in a micro-flow cell were developed. Due to a novel glutaminase with an activity optimum in the neutral pH range a direct monitoring of glutamine in mammalian cell culture medium could be performed. The glutamine bienzyme sensor was prepared by coimmobilization of glutaminase with glutamate oxidase within a photo patterned poly(2-hydroxyethyl methacrylate) (pHEMA) hydrogel membrane. The sensor response is linear in the concentration range of 55 mmol to 10 mmol glutamine/l. Additionally a glutamate biosensor is integrated on the sensor chip for difference measurement of possible glutamate interferences. The sensor chip can be used for at least 300 measurements without any alteration in the performance of its sensors. A new sensor chip with an integrated flow cell provides the possibility of simultaneous measurement of four different parameters at a cell volumina of 1 ml. Completing the microsystem a battery operated surface mounted device (SMD) potentiostat was developed to get a "lab on chip".

This chapter elaborates the ex vivo and in vivo evaluation of biosensors. The sensor device consists of a flexible polymer, carrier of 0.1 mm thickness with length of 60 mm and width of 0.7 mm. A Pt counter electrode, two Pt working electrode and a Ag/AgCl reference electrode can be used as electrochemical arrangement for glucose/H2U2, and LOD/H 2 O 2 measurement The thin film structure consists of evaporated 100 nm thick titanium-platinum sandwich layers for the counter, and working electrodes, and a 1 μm thick evaporated silver film which is chlorinated with FeCl 3 to obtain a Ag/AgCl reference electrode integrated on a 0.1 mm thick polyimide substrate. Areas to be insulated are covered by a polyimide film of about 2 μm. It is found that to prevent fouling of the electrodes, an electropolymerized 1,3-diamonobenzene film placed on the Pt-working electrodes was used. The used enzymes are immobilized in a photolithographycally patterned hydrogelmin.

This chapter discusses numerical simulation of membranized enzyme sensors. A lot of work is already done on the simulation of the steady state and transient performance of enzyme based sensors. However, little attention is paid to specific effects that have a serious impact on measuring accuracy and reliability of devices using enzyme loaded membranes. During the development of glucoseoxidase/H 2 O 2 and lactateoxidase/H 2 O 2 based glucose/lactate devices, some remarkable effects were observed which can not be explained using simple models. These effects include hyperlinear calibration characteristic, increasing sensitivity for decreasing oxygen concentrations, decreasing sensitivity for increasing enzyme activity load and some transient behavior like signal increase with two time constants. A model that gives a clear mechanistic view of oxidase based sensors operated under conditions close to cosubstrate limitation is presented. The effects are demonstrated and explained by fitting of the observed calibration graphs and transient signals with theoretical results obtained from an implicit difference simulation scheme.

A miniaturized thin-film biosensor integrated on a flexible substrate was developed for in vivo applications. A glucose sensor based on the measurement of H 2 O 2 produced by the enzyme glucose oxidase was created, with the possibility to perform differential measurements. Additionally, a solid state pH-sensor was integrated. The intended use of this device is the monitoring of glucose in the intensive care unit and the operation theatre, especially for neurosurgical applications. The glucose and pH-sensor was tested in buffer solutions, serum and whole blood.

Arrays of monolithically integrated Mach-Zehnder interferometers were fabricated by standard silicon technology and applied to the label-free real-time monitoring of biomolecular interactions. Chips accommodating 10 MZIs were functionalized with recognition biomolecules and encapsulated in wafer scale. Detection is based on Frequency-Resolved Mach-Zehnder Interferometry, a new concept that takes advantage of the broad-band input spectrum by monitoring the changes for every input frequency. The sensitivity of the device in terms of refractive index changes (Δn) was calculated using isopropanol/water solutions. A detection limit of Δn = 4 × 10(-6) was calculated. The bioanalytical capabilities of the device there demonstrated through model binding assays (biotin/streptavidin) as well as the detection of total prostate specific antigen in serum samples using devices coated with antigen-specific monoclonal antibody. Detection limits at the pM range were determined.

A system for continuous simultaneous ex vivo monitoring of blood glucose (b.g.) and subcutaneous tissue fluid glucose (s.g.) is presented. The system is based on two portable devices: (1) a continuous ambulatory blood sampler with a miniaturized thin-film glucose sensor in the sampling line and (2) a s.g. monitoring device using open tissue perfusion and measurement of glucose and conductivity for the calculation of absolute s.g. concentration. B.g. and s.g. are measured extracorporeally in a continuous manner with both devices. The system was evaluated in six healthy volunteers during an intravenous and a consecutive oral glucose tolerance test over 6 hours. >